Rigs drilling in the high Arctic may include sealed units to retain heat during drilling operations and rig moves. These rigs may move as a convoy of trailers towed by trucks and self-propelled units as they move between pads in the high Arctic. The typical rig move between pads may be several hundred yards or several miles. The complete rig may also move from well to well on the pad during drilling operations. During rig moves, the loads may be maintained below the tire capacity, bridge capacity, ice road capacity or other limiting factors. In some rigs, each of the 4 corners of the drilling modules may include 2 tires and two hydraulic drives all mounted onto a trunnion style suspension. The rig may include 4 trunnions in total and the rig may include a vertical hydraulic lift cylinder over each of the trunnions.
One style of rig for the Arctic drilling is a cantilevered style. In a cantilevered style rig, the drillfloor, mast, and well center may be cantilevered out over the well and wellhead to provide suitable vertical clearance for drilling operations. The cantilevered nature of the rig may enable the rig to traverse along a row of wells completing each well as it moves parallel to the wells.
These large drilling rigs and modules may be driven utilizing hydraulic motors. Hydraulic moving systems use several hundred gallons of hydraulic oil under pressures of 5000 psi and high flow rates to enable hydraulic motors to power each of the 8 tires. This hydraulic system may provide the tractive effort to move the rig. In an environmentally sensitive area such as the shoreline of the Arctic Ocean, the risk of a large environmental oil spill exists and may be caused by the high pressure and high flow rate of these hydraulic systems. The volume of hydraulic fluid used in these systems to move the rig is substantial and the risk of a hose failure or other substantial leak is great.
The steering mechanisms of these rigs may be known as Akermann steering and it may include a steering bar and hydraulic cylinders. This particular system of driving and steering can lead to tire scrubbing, notably while turning a corner, because the outside tires travel at a different RPM than the inside tires. These differing speeds of the tires at each corner of the drilling module cannot be controlled easily with hydraulics. Additional issues with the Akermann approach is that this steering system cannot rotate each of the 4 wheel sets 90 degrees without removal of the Akermann steering bar which can exceed 15 feet in length and 1000 pounds in weight. User intervention is commonly required and the Akerman steering bar is typically replaced with a different steering bar to provide for 90 degrees of travel. This current style of moving systems cannot enable the drilling module to travel at angles between the longitudinal direction and the transverse direction.
Current drilling modules have Akermann steering in the front and the back of the rig. The current steering geometry does not allow for the wheel sets at the front of the drilling module and the rear of the drilling module to steer together and point to one turn center for proper geometry, while the unit is negotiating a curve while travelling in a longitudinal direction. The turn center only works with current designs with either the front or rear steer acting alone, and pointing to the turn center, for proper geometry. This causes the turning radius of the drilling module vehicle to be larger, and more difficult to maneuver. Without proper steering on a tight curve, as the drilling module traverses the curve, tires may walk off the rims because each tire travels about a different center of rotation. This can be caused by the driver using both front and back steering mechanisms at the same time when each mechanism is not designed for such use. Thus, each tire follows a different radial path rather than a series of concentric radial paths that all converge to the same center point. The tire scrub produced by a lack of steering geometry with all wheel steering, can cause the tires to separate from the rims.
The tires on these rigs may be 40×57 tires and may have a pressure of 120 psi while loaded with over 100 tons per tire. Any excessive flexing of a tire while it is moving, produces heat. Excess heat can cause a tire failure. A tire failure of this size of tire could rupture the moving system hydraulic hoses, and cause an environmental spill on the tundra next to the Arctic Ocean. Moreover, this can result in a dangerous situation where, for example, an explosive tire deflation caused by tire/rim separation occurs and/or stability is reduced. In particular, where the rig includes a very tall vertically extending mast riding on it, the risk of overturning and catastrophic failure may be great. The overall height of the drilling module may exceed 230 feet and placing such a structure at risk of toppling is a grave concern.